Mechanoreception

Stretch-activated ion channels

In sensory cells, activate w/ change in pressure, must reach threshold pressure change/pressure diff across PM

Diff types of strech

Diff cells respond to diff types of stretch eg shear, stretch, fluid, indent, physical touch, some cells lie across elastometric pillars that stretch cells w/ stimuli

How stretch activated channels open

1) tether model \*(most evidence): stretch cell is tethered by integral membrane proteins to extracellular matrix, pull on tether opens channel

2) bilayer model - tension in PM opens channel

3) indirect gating - diff protein sensitive to stretch opens ion channel

some channels only move certain ions but some move more

Hair cell embedded in epithelial sheet

Directional signaling

Base rate of AP firing w/ no signal, AP rate inc with movement in 1 direction, AP rate dec with movement in other direction

Signaling steps

Stretch gated ion channels opened more, K+ rushes in, causes change in Em, change opens more Ca+ channels, more synaptic vesicles/neurotransmitters=more AP

opposite for dec in firing rate

Sensitivity

Force/direction of vector affects # of channels that open, amount change in Em affects # Ca+ channels that open

Utricle

in middle of inner ear, connected to semicircular ducts

Macula

Circle of epithelial cells, hair cells embedded, gelatenus later w/ calcium carbonate crystals---gravity tilts crystals, deforms hair cells, verstibulochchlear nerve detects gravity

Semi-circular ducts

swellings at end, connected to utricle, filled w/ fluid that sloshes around, deforms cupula

Cupula

Epithelial cells w/ hair cells embedded w/ gelatenous cupula, as head rotates fluid deforms cupula + hair cells in opposite directions, different canals bend more in some directions than others